Acid-alcohol extracts of duck pancreas, duodenum, jenunum and ileum were applied to columns of Sephadex G50, and the fractions obtained after chromatography assayed for glucagon in a radioimmunological technique. The molecular size was estimated by comparing the elution volume of the glucagon-containing eluates, with reference values obtained with pure proteins. Two types of glucagon were found in the pancreas; the one, having a molecular weight equivalent to crystalline glucagon, and the other with approximately the double, namely 6,000. Considerable quantities of this "large" glucagon, but none of the smaller counterpart, were recovered from both jejunum and ileum extracts. Neither of the glucagon forms could be consistently found in investigations of the duodenum. The results may mean that not only the pancreas, but also the intestine, contribute to the total level of glucagon found in blood. Furthermore, the pancreatic secretion may be a mixture of two molecular species, while that originating from the jejunum and ileum would contain uniquely the larger analogue.